1. Field of the Invention
The present invention relates to image display devices such as organic electroluminescent (EL) display devices.
2. Description of the Background Art
There have been proposed image display devices using organic EL elements that have a function of emitting light as a result of recombination of holes and electrons injected into an emissive layer.
In this type of image display device, a thin film transistor (hereinafter referred to as a “TFT”) formed of, e.g., amorphous silicon or polycrystalline silicon, and an organic light-emitting diode (hereinafter referred to as an “OLED”); which is one of organic EL elements, constitutes each pixel, and pixels are arranged in a matrix. By setting an appropriate electric current for each pixel, the luminance of each pixel is controlled, so that a desired image is displayed.
In this respect, refer to R. M. A. Dawson, et al. (1998), Design of an Improved Pixel for a Polysilicon Active-Matrix Organic LED Display, SID 98 Digest, pp. 11-14, and S. Ono, et al. (2003), Pixel Circuit for a-Si AM-OLED, Proceedings of IDW '03, pp. 255-258.
In an image display device as described above, a plurality of pixels share feeders. The feeders have a gradual voltage drop, which causes an applied voltage to each pixel to vary depending on the voltage drop, and luminance non-uniformity may occur in a displayed image. For example, in a feeding system of supplying a predetermined voltage from the lower side to pixels arranged in a matrix, an applied voltage to an organic EL device in a pixel located on the upper side is lower than that in a pixel located on the lower side. Thus, luminance non-uniformity is recognized in which luminance gradually decreases as the distance of a pixel and the feeder lines increases.
Note that it is possible to make equal the length or resistance of feeders to each pixel so that all pixels have the same voltage drop, but such methods should be avoided because they limit the design flexibility and increase the manufacturing costs.